Ducted fan air-vehicles typically have at least one ducted fan and a fan engine to drive the fan blades. These vehicles may be preprogrammed to perform operations autonomously, or they may be controlled by a human operator. Ducted fan air-vehicles are well known for excellent stationary hovering aerodynamic performance and have the ability of forward flight.
Ducted fan air-vehicles have become increasingly used in a variety of applications. Such applications include military situations, such as surveillance, reconnaissance, target acquisition, data acquisition, communications relay, decoy, harassment, or supply flights. These vehicles are also used in a growing number of civilian applications, such as fire fighting, police observation, reconnaissance support in natural disasters, and scientific research.
Many of these applications require that the ducted fan air-vehicles carry a variety of payloads or cargo. For example, ducted fan air-vehicles may need to carry visual sensors, infrared sensors, cameras, radio communication devices, inertial sensor units, ground level sensor units, and/or other payloads. This cargo may cause a shift in the center of gravity, which can create negative interference with airflow characteristics inside the duct by blocking air intake and exhaust, and create additional drag on the vehicle when the vehicle is in forward flight. When the vehicle CG changes, the center of lift needs to change in order have the aerodynamic forces balance the forces due to gravity acting on the vehicle.
Ducted fan air-vehicles are designed to have a specific center of gravity in order to be effective and controllable. These vehicles are sensitive to even slight weight redistributions, i.e. any change to the weight distribution can impact the airflow within the duct. Accordingly, even slight modifications to the cargo/payload can negatively impact performance specifically stability. Differing weight distributions are typically dealt with by either developing a new variation of the vehicle or developing an entirely new aircraft for each type of cargo. Both designing a new aircraft and developing a variation of the vehicle are time-consuming and costly.
Furthermore, some flight conditions and mere forward flight can interfere with the desired airflow characteristics and, by implication, flight control and performance. It is important to design the vehicle with the proper CG location (or range of locations), just as for a fixed wing aircraft.